The present invention relates generally to blood filter devices for temporary placement in a blood vessel to capture embolic material, and more particularly to a cannula device having an associated blood filter for placement in a blood vessel to carry blood to an artery from a bypass-oxygenator system and to entrap embolic material in the vessel. More particularly, the invention relates to a blood filter device to be placed in the aorta during cardiac surgery. The present invention also relates to methods for temporarily filtering blood to entrap and remove embolic material and, more particularly, to methods for protecting a patient from embolization which has been caused by procedures such as incising, clamping, and clamp release which can dislodge atheromatous material from the artery.
There are a number of known devices designed to filter blood. The vast majority of these devices are designed for permanent placement in veins, in order to trap emboli destined for the lungs. For example, Kimmell, Jr., U.S. Pat. No. 3,952,747 (this and all other references cited herein are expressly incorporated by reference as if fully set forth in their entirety herein), discloses the so-called Kimray-Greenfield filter. This is a permanent filter typically placed in the vena cava comprising a plurality of convergent legs in a generally conical array, which are joined at their convergent ends to an apical hub. Each leg has a bent hook at its end to impale the internal walls of the vena cava.
Cottenceau et al., U.S. Pat. No. 5,375,612, discloses a blood filter intended for implantation in a blood vessel, typically in the vena cava. This device comprises a zigzagged thread wound on itself and a central strainer section to retain blood clots. This strainer section comprises a meshed net and may be made from a biologically absorbable material. This device is also provided with attachment means which penetrate into the wall of the vessel.
Gunther et al., U.S. Pat. No. 5,329,942, discloses a method for filtering blood in the venous system wherein a filter is positioned within a blood vessel beyond the distal end of a catheter by a positioning means guided through the catheter. The positioning means is locked to the catheter, and the catheter is anchored to the patient. The filter takes the form of a basket and is comprised of a plurality of thin resilient wires. This filter can be repositioned within the vessel to avoid endothelialization within the vessel wall.
Similarly, Lefebvre, French Patent No. 2,567,405, discloses a blood filter for implantation by an endovenous route into the vena cava. The filter is present in the form of a cone, and the filtering means may consist of a flexible metallic grid, or a flexible synthetic or plastic grid, or a weave of synthetic filaments, or a non-degradable or possibly bio-degradable textile cloth. In order to hold the filter within the vein, this device includes flexible rods which are sharpened so that they may easily penetrate into the inner wall of the vena cava.
There are various problems associated with permanent filters. For example, when a filter remains in contact with the inner wall of the vena cava for a substantial period of time, endothelialization takes place and the filter will subsequently become attached to the vena cava. This endothelialization may cause further occlusion of the vessel, thereby contributing to the problem the filter was intended to solve. Except for the Gunther device, these prior art filters do not address this problem.
A temporary venous filter device is disclosed in Bajaj, U.S. Pat. No. 5,053,008. This device treats emboli in the pulmonary artery which, despite its name, is in fact a vein. The Bajaj device is an intracardiac catheter for temporary placement in the pulmonary trunk of a patient predisposed to pulmonary embolism because of hip surgery, stroke or cerebral hemorrhage, major trauma, major abdominal or pelvic surgery, neurosurgery, neoplasm, sepsis, cardiorespiratory failure or immobilization.
The Bajaj device includes an umbrella made from meshwork which traps venous emboli before they reach the lungs. This device can also lyse emboli with a thrombolytic agent such as tissue plasminogen activator (TPA), destroy emboli with high velocity ultrasound energy, and remove emboli by vacuum suction through the lumen of the catheter. This very complex device is designed for venous filtration and is difficult to justify when good alternative treatments exist.
There are very few intravascular devices designed for arterial use. A filter that functions not only in veins, but also in arteries must address additional concerns because of the hemodynamic differences between arteries and veins. Arteries are much more flexible and elastic than veins and, in the arteries, blood flow is pulsatile with large pressure variations between systolic and diastolic flow. These pressure variations cause the artery walls to expand and contract. Blood flow rates in the arteries vary from about 1 to about 5 L/min.
Ginsburg, U.S. Pat. No. 4,873,978, discloses an arterial device. This device includes a catheter that has a strainer device at its distal end. This device is normally used in conjunction with non-surgical angioplastic treatment. This device is inserted into the vessel downstream from the treatment site and, after the treatment, the strainer is collapsed around the entrapped emboli, and the strainer and emboli are removed from the body. The Ginsburg device could not withstand flow rates of 5 L/min. It is designed for only small arteries and therefore could not capture emboli destined for all parts of the body. For example, it would not catch emboli going to the brain.
Ing. Walter Hengst GmbH and Co, German Patent DE 34 17 738, discloses another filter which may be used in the arteries of persons with a risk of embolism. This filter has an inherent tension which converts the filter from the collapsed to the unfolded state, or it can be unfolded by means of a folding linkage system. This folding linkage system comprises a plurality of folding arms spaced in parallel rows along the longitudinal axis of the conical filter (roughly similar to branches on a tree). The folding arms may be provided with small barbs at their projecting ends intended to penetrate the wall of the blood vessel to improve the hold of the filter within the vessel.
Moreover, da Silva, Brazil Patent Application No. PI9301980A, discusses an arterial filter for use during certain heart operations where the left chamber of the heart is opened. The filter in this case is used to collect certain particles not removed on cleaning the surgical site.
What is needed is a simple, safe blood filter for temporary use. For example, a temporary arterial device for use during surgery that neither complicates nor lengthens the surgical procedure would be desirable. Existing prior art devices are inadequate for this purpose.
The present invention relates to blood filter devices and methods of filtering blood. The devices of the present invention are adapted to filter embolic material from the blood. Embolic material or foreign matter is any particulate matter which may cause complications in the body if allowed to travel freely in the bloodstream. This particulate matter includes but is not limited to atheromatous fragments or material, and fat.
In one embodiment, the device includes four major elements: a mesh, which filters blood flowing in a blood vessel; an insertion tube adapted for placing the mesh into and removing it from the blood vessel; an umbrella frame adapted for connecting the mesh to the insertion tube and for positioning and maintaining the mesh in a position wherein blood passes therethrough; and a means for opening and closing the umbrella frame.
In another embodiment, the device includes three major elements: a mesh, which filters blood flowing in a blood vessel; an umbrella frame adapted for positioning and maintaining the mesh in a position wherein blood passes therethrough; and a means for opening and closing the umbrella frame. The umbrella frame is affixed to a cannula which is inserted into the blood vessel. In alternative embodiments, the mesh additionally may be provided to cover the end of the cannula if necessary. This additional mesh simply may be an extension of the mesh of the second preferred embodiment, or it may be a separate mesh located either at the end of the cannula or within the cannula.
In another embodiment, the device includes four major elements: a continuous mesh for filtering blood flowing within a blood vessel; an inflatable donut-shaped balloon adapted to open and close the mesh; a plurality of tie lines to hold the mesh and balloon in place within the bloodstream; and an actuation assembly. In a preferred embodiment, the mesh is cone-shaped and four tie lines attached to the inflatable balloon are employed to hold the balloon and the mesh in place for filtering.
In still another embodiment, the device may include an arterial cannula disposed within a pressurizing cannula. The pressurizing cannula has a proximal region, a distal region, and an intermediate region therebetween, which intermediate region includes a first lumen passing from the proximal to distal end and shaped to receive a cannula for blood supply. The distal region may include an associated filter comprising a mesh which may have a substantially conical shape in an expanded condition and which may be contracted to a smaller, substantially cylindrical shape. The proximal end of the mesh may be attached to an inflatable, donut-shaped balloon or inflation seal adapted to open and close the mesh. The inflation seal-mesh assembly may be attached at its proximal end to the pressurizing cannula and, at its distal end, may optionally include any of an unbroken continuous mesh, a mesh attached to a distal region of the cannula for blood supply, and a mesh attached to a distal region of the pressurizing cannula. The pressurizing cannula will generally include means for inflating and deflating the inflation seal.
In another embodiment, the device includes a mesh, an arterial cannula, a blood flow diffuser and a structure adapted to open and close the mesh within the blood vessel, such as an umbrella frame or inflatable balloon. The blood flow diffuser may be located inside or outside of the arterial cannula. In both the intra-cannula and extra-cannula diffuser embodiments, the flow diffuser can be located either proximal or distal to the mesh.
In another embodiment, the device includes a sleeve which, when unrolled, captures the mesh and the expansion frame adapted to open and close the mesh. In one embodiment the sleeve may be actuated by control lines which control the unrolling and rolling-up of the sleeve. The captured structure may be an umbrella frame adapted for positioning and maintaining the mesh in a position wherein blood passes therethrough. Alternatively, the captured structure is an inflatable balloon.
In still another embodiment, the device includes a cannula made in part of a deformable (e.g.) elastomeric material such that the deformable part of the cannula collapses to absorb the mesh and the corresponding adapted structure upon mesh closure, thereby reducing the profile of the instrument for vessel introduction.
The methods of the present invention relate to filtering blood flowing within a blood vessel, particularly to entrap embolic material, thereby protecting a patient from embolization. In accordance with one aspect of the method of the invention, a patient is protected from embolization during surgery while performing a procedure affecting a region of an artery of the patient wherein the artery includes foreign matter on an inside surface thereof at least a portion of which is dislodged as a result of mechanical or other forces applied during the procedure, by deploying a removable filtration device in a blood vessel downstream of one affected region of the artery to entrap the dislodged foreign matter.
In other embodiments, the methods of the present invention generally include the following steps: introducing a mesh into a blood vessel to entrap embolic material or foreign matter in the blood, positioning the mesh, if necessary, and removing the mesh and the entrapped foreign matter from the blood vessel. Additionally, visualization techniques including transcranial doppler ultrasonography, transesophageal echocardiography, epicardiac echocardiography, and transcutaneous or intravascular ultrasonography in conjunction with the procedure may be used to ensure effective filtration.
In a preferred method, blood is filtered during cardiac surgery, in particular during cardiac bypass surgery, to protect a patient from embolization. In this method, the mesh is positioned in the aorta where it filters blood before it reaches the carotid arteries, brachiocephalic trunk, and left subclavian artery.
The present invention was developed, in part, in view of a recognition of the occurrence of embolization during cardiac surgery. Emboli are frequently detected in cardiac surgery patients and have been found to account for neurologic, cardiac and other systemic complications. Specifically, embolization appears to contribute significantly to problems such as strokes, lengthy hospital stays and, in some cases, death. Of the patients undergoing cardiac surgery, 5-10% experience strokes and 30% become cognitively impaired. In addition, it has been recognized that embolization is often the result of procedures performed on blood vessels such as incising, clamping, and cannulation, wherein mechanical or other force is applied to the vessel. See, for example, Barbut et al., xe2x80x9cCerebral Emboli Detected During Bypass Surgery Are Associated With Clamp Removal,xe2x80x9d Stroke, 25(12):2398-2402 (1994), which is incorporated herein by reference in its entirety. These procedures are commonly performed in many different types of surgery including cardiac surgery, coronary artery surgery including coronary artery bypass graft surgery, aneurysm repair surgery, angioplasty, atherectomy, and endarterectomy, including carotid endarterectomy. It has also been recognized that reintroducing blood into blood vessels with a cannula during these procedures can dislodge plaque and other emboli-creating materials as a result of blood impinging upon the vessel wall at high velocities. See, for example, Cosgrove et. al., Low Velocity Aortic Cannula, U.S. Pat. No. 5,354,288. Finally, it has been found that the occurrence of embolization is more likely in certain types of patients. For example, embolization occurs more frequently in elderly patients and in those patients who have atheromatosis. In fact, atheromatous embolization, which is related to severity of aortic atheromatosis, is the single most important contributing factor to perioperative neurologic morbidity in patients undergoing cardiac surgery.
Embolic material, which has been detected at 2.88 mm in diameter, will generally range from 0.02 mm (20 xcexcm) to 5 mm, and consists predominantly of atheromatous fragments dislodged from the aortic wall and air bubbles introduced during dissection, but also includes platelet aggregates which form during cardiac surgery. See Barbut et al., xe2x80x9cDetermination of Embolic Size and Volume of Embolization During Coronary Artery Bypass Surgery Using Transesophageal Echocardiography,xe2x80x9d J. Cardiothoracic Anesthesia (1996). These emboli enter either the cerebral circulation or systemic arterial system. Those entering the cerebral circulation obstruct small arteries and lead to macroscopic or microscopic cerebral infarction, with ensuing neurocognitive dysfunction. Systemic emboli similarly cause infarction, leading to cardiac, renal, mesenteric, and other ischemic complications. See Barbut et al., xe2x80x9cAortic Atheromatosis And Risks of Cerebral Embolization,xe2x80x9d Journal of Cardiothoracic and Vascular Anesthesia 10(1):24-30 (1996), which is incorporated herein by reference in its entirety.
Emboli entering the cerebral circulation during coronary artery bypass surgery have been detected with transcranial Doppler ultrasonography (TCD). TCD is a standard visualization technique used for monitoring emboli in the cerebral circulation. To detect emboli using TCD, the middle cerebral artery of a bypass patient is continuously monitored from aortic cannulation to bypass discontinuation using a 2 MHZ pulsed-wave TCD probe (Medasonics-CDS) placed on the patient""s temple at a depth of 4.5 to 6.0 cm. The number of emboli is determined by counting the number of embolic signals, which are high-amplitude, unidirectional, transient signals, lasting less than 0.1 second in duration and associated with a characteristic chirping sound.
TCD is useful in analyzing the relationship between embolization and procedures performed on blood vessels. For example, the timing of embolic signals detected by TCD have been recorded along with the timing of procedures performed during open or closed cardiac surgical procedures. One of these procedures is cross-clamping of the aorta to temporarily block the flow of blood back into the heart. It has been found that flurries of emboli are frequently detected after aortic clamping and clamp release. During the placement and removal for the clamps, atheromatous material along the aortic wall apparently becomes detached and finds its way to the brain and other parts of the body. Similarly, flurries of emboli are also detected during aortic cannulation and inception and termination of bypass.
Transesophageal echocardiography (TEE), another standard visualization technique known in the art, is significant in the detection of conditions which may predispose a patient to embolization. TEE is an invasive technique, which has been used, with either biplanar and multiplanar probes, to visualize segments of the aorta, to ascertain the presence of atheroma. This technique permits physicians to visualize the aortic wall in great detail and to quantify atheromatous aortic plaque according to thickness, degree of intraluminal protrusion and presence or absence of mobile components, as well as visualize emboli within the vascular lumen. See, for example, Barbut et al., xe2x80x9cComparison of Transcranial Doppler and Transesophageal Echocardiography to Monitor Emboli During Coronary Bypass Surgery,xe2x80x9d Stroke 27(1):87-90 (1996) and Yao, Barbut et al., xe2x80x9cDetection of Aortic Emboli By Transesophageal Echocardiography During Coronary Artery Bypass Surgery,xe2x80x9d Journal of Cardiothoracic Anesthesia 10(3):314-317 (May 1996), and Anesthesiology 83(3A):A126 (1995), which are incorporated herein by reference in their entirety. Through TEE, one may also determine which segments of a vessel wall contain the most plaque. For example, in patients with aortic atheromatous disease, mobile plaque has been found to be the least common in the ascending aorta, much more common in the distal arch and most frequent in the descending segment. Furthermore, TEE-detected aortic plaque is unequivocally associated with stroke. Plaque of all thickness is associated with stroke but the association is strongest for plaques over 4 mm in thickness. See Amarenco et al., xe2x80x9cAtherosclerotic disease of the aortic arch and the risk of ischemic stroke,xe2x80x9d New England Journal of Medicine, 331:1474-1479 (1994).
Another visualization technique, intravascular ultrasound, is also useful in evaluating the condition of a patient""s blood vessel. Unlike the other techniques mentioned, intravascular ultrasound visualizes the blood vessel from its inside. Thus, for example, it is useful for visualizing the ascending aorta overcoming deficiencies of the other techniques. In one aspect of the invention, it is contemplated that intravascular ultrasound is useful in conjunction with devices disclosed herein. In this way, the device and visualizing means may be introduced into the vessel by means of a single catheter.
Through visualization techniques such as TEE epicardial aortic ultrasonography and intravascular ultrasound, it is possible to identify the patients with plaque and to determine appropriate regions of a patient""s vessel on which to perform certain procedures. For example, during cardiac surgery, in particular, coronary artery bypass surgery, positioning a probe to view the aortic arch allows monitoring of all sources of emboli in this procedure, including air introduced during aortic cannulation, air in the bypass equipment, platelet emboli formed by turbulence in the system and atheromatous emboli from the aortic wall. Visualization techniques may be used in conjunction with a blood filter device to filter blood effectively. For example, through use of a visualization technique, a user may adjust the position of a blood filter device, and the degree of actuation of that device as well as assessing the efficacy of the device by determining whether foreign matter has bypassed the device.
It is an object of the present invention to eliminate or reduce the problems that have been recognized as relating to embolization. The present invention is intended to entrap and remove emboli in a variety of situations. For example, in accordance with one aspect of the invention, blood may be filtered in a patient during procedures which affect blood vessels of the patient. The present invention is particularly suited for temporary filtration of blood in an artery of a patient to entrap embolic debris. This in turn will eliminate or reduce neurologic, cognitive, and cardiac complications helping to reduce length of hospital stay. In accordance with another aspect of the invention, blood may be filtered temporarily in a patient who has been identified as being at risk for embolization.
As for the devices, one object is to provide simple, safe and reliable devices that are easy to manufacture and use. A further object is to provide devices that may be used in any blood vessel. Yet another object is to provide devices that will improve surgery by lessening complications, decreasing the length of patients"" hospital stays and lowering costs associated with the surgery. See Barbut et al., xe2x80x9cIntraoperative Embolization Affects Neurologic and Cardiac Outcome and Length of Hospital Stay in Patients Undergoing Coronary Bypass Surgery,xe2x80x9d Stroke (1996).
The devices disclosed herein have the following characteristics: can withstand high arterial blood flow rates for an extended time; include a mesh that is porous enough to allow adequate blood flow in a blood vessel while capturing mobile emboli; can be used with or without imaging equipment; remove the entrapped emboli when the operation has ended; will not dislodge mobile plaque; and can be used in men, women, and children of varying sizes.
As for methods of use, an object is to provide temporary filtration in any blood vessel and more particularly in any artery. A further object is to provide a method for temporarily filtering blood in an aorta of a patient before the blood reaches the carotid arteries and the distal aorta. A further object is to provide a method for filtering blood in patients who have been identified as being at risk for embolization. Yet a further object is to provide a method to be carried out in conjunction with a blood filter device and visualization technique that will assist a user in determining appropriate sites of filtration. This visualization technique also may assist the user in adjusting the blood filter device to ensure effective filtration. Yet a further object is to provide a method for filtering blood during surgery only when filtration is necessary. Yet another object is to provide a method for eliminating or minimizing embolization resulting from a procedure on a patient""s blood vessel by using a visualization technique to determine an appropriate site to perform the procedure. Another object is to provide a method for minimizing incidence of thromboatheroembolisms resulting from cannula procedures by coordinating filtration and blood flow diffusion techniques in a single device. Another object is to provide a method of passing a filtering device through a vessel wall by first capturing the mesh filter with a sleeve so as to reduce the device profile. For a related discussion of subject matter pertaining to a filter cannula, the reader is referred to co-pending U.S. application Ser. No. 08/640,015, filed Apr. 30, 1996, U.S. application Ser. No. 08/584,759, filed Jan. 9, 1996, U.S. application Ser. No. 08/580,223, filed Dec. 28, 1995, and U.S. application Ser. No. 08/553,137, filed Nov. 7, 1995, all of which are expressly incorporated herein by reference in their entirety.